The *_ipic and *_mpic handlers are almost identical - the only
difference is that the latter end with an unconditional
chip->irq_eoi() call. Since IPIC does not have ->irq_eoi, we can
reduce some code duplication by calling irq_eoi conditionally.

This is similar to what is already done in mpc8xxx_gpio_irq_cascade().

This leaves the functions slightly misnamed, but that will be fixed in
a subsequent patch.
Reviewed-by: Timur Tabi <timur@kernel.org>
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Li Yang <leoyang.li@nxp.com>